# [LeetCode] Find Bottom Left Tree Value 寻找最左下树结点的值

Given a binary tree, find the leftmost value in the last row of the tree.

Example 1:

Input:

2
/ \
1   3

Output:
1


Example 2:

Input:

1
/ \
2   3
/   / \
4   5   6
/
7

Output:
7


Note: You may assume the tree (i.e., the given root node) is not NULL.

class Solution {
public:
int findBottomLeftValue(TreeNode* root) {
if (!root) return 0;
int max_depth = 1, res = root->val;
helper(root, 1, max_depth, res);
return res;
}
void helper(TreeNode* node, int depth, int& max_depth, int& res) {
if (!node) return;
if (depth > max_depth) {
max_depth = depth;
res = node->val;
}
helper(node->left, depth + 1, max_depth, res);
helper(node->right, depth + 1, max_depth, res);
}
};

class Solution {
public:
int findBottomLeftValue(TreeNode* root) {
if (!root) return 0;
int res = 0;
queue<TreeNode*> q;
q.push(root);
while (!q.empty()) {
int n = q.size();
for (int i = 0; i < n; ++i) {
TreeNode *t = q.front(); q.pop();
if (i == 0) res = t->val;
if (t->left) q.push(t->left);
if (t->right) q.push(t->right);
}
}
return res;
}
};

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